NieR

This is part of the story and cannot be missed. The objective of part 2 of the game is to gather these 5 key fragments which the game holds your hand to lead you to. You can usually pick between 2 different ones to go after at any point, which will cause the quest to start for one specific key. You will find the first key fragment after defeated Gretel at the top of the Lost Temple. After that one you can start to pick which one you want to go after next by choosing between two options that are clearly presented on screen.

The easiest key fragment after the first one is found in the Forest of Myth. Simply talk to the elder then interact with the sparkle in front of the big tree and you will go into a text story sequence. At the end of the tree's story it will ask you two riddles related to the two stories you read. These are not static- they are slightly randomized, so don't just skip past all the text. What you need to note is the color of the girl's eyes in the story about the sick boy- that is the color of envy which is what the first riddle will ask you. The second detail you need to note is the number of companions who died during the female warriors battle in the second story. The last riddle simply asks you something along the lines of what is the most important thing in the world, and all three answers are correct. If you answered the riddles correctly, you get the key. No fighting involved.

After that you can choose to investigate the junk heap or go back and talk to Popola. If you choose to go see Popola she will show you a letter from the Aerie chieftan. You go to the Aerie, talk to the chieftan through his door- he won't deal with you. You are prompted to investigate the town. What you need to do is climb over to the big platform with the 4 merchants on it. (you can see them as big white dots on your map of the area) There will be a guard standing there and when you talk to him you will trigger a long battle afterwhich the Aerie will be completely destroyed. If you have any business there, take care of it before you talk to that guard. Besides the DLC, it is the only place to get eagle eggs of which you need 4 of if you plan to fully forge all your weapons to level 4. The weapon merchant there also sells some weapons not found elsewhere. The eggs will almost certainly take you hours to obtain, but you can come back and harvest the eggs and buy the weapons on later playthroughs at your leisure, but once you talk to the guard, you will not be able to do anything in the Aerie for the remainder of that playthrough.

The last two key fragments are in the junk heap and a chain leading you to facade. No inconvenient consequences are involved with completing these like with the Aerie.

It should be noted that as you collect more key fragments, stronger varieties of shades will take the place of weaker ones in many areas. More quests will appear as you complete key fragments as well. There are no quests involving the Aerie in part 2 so you don't have to worry about that. Once you have all 5 fragments you can do whatever you like for as long as you want, but once you enter the shadowlord's castle by unsealing the door at the top of the lost temple, you cannot go back- it tells you that very clearly with a prompt before you open the door giving you the option to wait and come back later. Of course, if you clear the castle you will be able to save a completed game and start another newgame+ type playthrough which gives further insight into the plot of the game and leads to different endings.

WARNING: Once you have finished your second playthrough of part 2, on the next playthrough you will only have the options to proceed to endings C and D at the end of the shadowlord's castle. D will erase all of your data. You must have all the weapons in the game in your possession to have the option of choosing ending C which will allow you to start yet another playthrough, on which you can continue to pick ending C as long as you want for as many more playthroughs as you like if you are just crazy about playing through the second half the story.

Here is the solution I wrote up for ending D detailing exactly how you probably want to proceed through your later playthroughs to save yourself a good deal of time and possibly avoid the chance of completely screwing yourself over.